APPLICATION NOTE
2
(8)
Measuring S-Parameter Data from the PSpice Probe
Where
V1/I1 is the input impedance Z.
S21 is the forward transmission ratio and is defined as the ratio b2/a1.
If the input and output load impedances of the circuit are the same, then S21 is the voltage measured at the
output multiplied by 2. If the incident wave at the input is set to zero, then the equations reduce to
b1 = S12a2
b2 = S22a2
Measuring S-Parameter Data from the PSpice Probe
To make all of the necessary measurements, two sub schematics are required. These sub schematics, made in
Allegro Design Entry CIS (Capture CIS), are shown in Figure.1 and Figure. 2.
Figure 1: XMITS circuit
